1. Field of the Invention
The present invention relates to a state determination device for an internal combustion engine that includes a fuel injection mechanism (in-cylinder injector) injecting fuel into a cylinder and a fuel injection mechanism (intake manifold injector) injecting fuel into an intake manifold or an intake port, and more particularly to a technique to determine a state of a detection unit (airflow meter) that detects an intake air amount based on a state of the fuel injection mechanism.
2. Description of the Background Art
An internal combustion engine provided with an intake manifold injector for injecting fuel into an intake manifold and an in-cylinder injector for injecting fuel into a combustion chamber is known.
Japanese Patent Laying-Open No. 2000-274296 discloses a fuel injection control device for an internal combustion engine, the internal combustion engine including a main fuel injection valve directly injecting fuel into a combustion chamber of each cylinder and an auxiliary fuel injection valve in an intake manifold, located upstream of a branch portion of each cylinder, for diagnosing shortage in an amount of fuel injection from the auxiliary fuel injection valve. The fuel injection control device disclosed in Japanese Patent Laying-Open No. 2000-274296 controls a direct injection spark ignition type internal combustion engine including the main fuel injection valve directly injecting fuel into the combustion chamber. The internal combustion engine is provided with the auxiliary fuel injection valve capable of injecting fuel into the intake manifold, separately from the main fuel injection valve, and the fuel injection control device includes a switch control unit actuating the auxiliary fuel injection valve under a prescribed operation condition so as to supply fuel to an engine through the main fuel injection valve and the auxiliary fuel injection valve at a ratio set therebetween, an air-fuel ratio detection unit detecting an air-fuel ratio under the prescribed operation condition, and an auxiliary fuel injection valve diagnosing unit diagnosing abnormality of the auxiliary fuel injection valve based on the air-fuel ratio detected under the prescribed operation condition.
According to the fuel injection control device disclosed in this publication, when an amount of fuel injection from the auxiliary fuel injection valve is insufficient under the prescribed operation condition, the air-fuel ratio becomes leaner relative to a preset air-fuel ratio. The air-fuel ratio detection unit detects such change in the air-fuel ratio, so that the auxiliary fuel injection valve diagnosing unit can diagnose the auxiliary fuel injection valve as abnormal.
The fuel injection control device according to Japanese Patent Laying-Open No. 2000-274296 diagnoses solely abnormality of the auxiliary fuel injection valve. Meanwhile, abnormality of the main fuel injection valve can similarly be diagnosed by observing the air-fuel ratio under an operation condition in which fuel is injected solely from the main fuel injection valve. In general, the amount of fuel injection is determined based on an intake air amount in the internal combustion engine. Accordingly, when an erroneous intake air amount is detected due to abnormality in the airflow meter (an intake air amount detection sensor) as well, the air-fuel ratio may deviate from a desired air-fuel ratio. Japanese Patent Laying-Open No. 2000-274296, however, includes no description of determination of a state of the intake air amount detection sensor.